In recent years, demand for portable terminal devices such as a cellular phone and a laptop computer is increasing. In particular, development of a thin portable terminal device having a commodity value of acoustic functions such as television telephone, moving picture reproduction, and hands-free telephone function is being advanced.
There is a portable terminal device of a type in which first and second casings are coupled to each other via a biaxial hinge. The biaxial hinge axially supports the first and second casings about a first axis so that they are turnable, and axially supports the second casing with respect to the first casing turnably about a second axis which crosses the first axis. In the case of providing a display device in the second casing in such a portable terminal device of a biaxial hinge type, as the second casing turns about the second axis, the orientation of a display screen of the display device also turns (for example, Patent Document 1).
Patent Document 2 describes a technique of forming a waveguide which guides a sound wave generated from a speaker, in a hinge of a foldable cellular phone. Patent Document 3 describes a technique of forming a waveguide for collecting voice by a microphone in a hinge of a wireless telephone.